//字符串 - 二进制求和
class Solution {
public:
    string addBinary(string a, string b) {
        string ret;
        int cur1 = a.size() - 1, cur2 = b.size() - 1, t = 0;
        while(cur1 >= 0 || cur2 >= 0 || t)
        {
            if(cur1 >= 0) t += (a[cur1--] - '0');
            if(cur2 >= 0) t += (b[cur2--] - '0');
            ret += (t % 2 + '0');
            t /= 2;
        }
        reverse(ret.begin(), ret.end());
        return ret;
    }
};
